There are presently available on the market today a wide range of folders ranging from the very low priced up to the more expensive ring binder type folder. These folders fall in two basic categories which are the loose leaf version and the permanently bound type version where it is difficult, if not impossible, to add or change sheets without requiring special machines.
According to the former version with which the present invention is concerned, there are presently available a number of different types of loose leaf folders. For example, there are the folders comprising paper covers and metal tangs sold under the trade marks DUOTANG and ACCO FASTENERS. There is also available that plastic clamp type loose leaf folder which uses an extruded plastic slide bar in the form of a U-shaped channel used to bind sheets together. Both of the above type systems are somewhat difficult to work with. In the duotang-type system, the tangs or fasteners are deformed after numerous uses and in the latter slide bar-type bar system, the bar must be tightly locked in position in which case the sheets are tightly held at the binding edge and resist opening. Any pressure to open the pages tends to dislodge the slide bar from its binding position.
Another system of which most people are aware of is the ring-type binder. However, again, the ring binder is high in cost and is generally not acceptable for use with only 20 to 30 pages.
A very easy and inexpensive system is the ball and socket or dome-type arrangement as shown in U.S. Pat. No. 3,768,838 issued Oct. 30th, 1973 to Shibata. According to the Shibata system, as well as most other conventional dome systems, a generally rounded head is secured into a generally rounded opening of lesser diameter than the head. The head itself is collapsible either as a result of the material from which the head is made or due to the provision of slots in the head which permit its inward collapsing as it is forced into the opening. However, because either the head or the socket opening or both are relatively resilient to permit fastening, the securing is not often as positive as is required to effectively bind the arrangement together. Furthermore, anyone who has worked with these dome-type fasteners will appreciate that if the head is not perfectly aligned with the socket getting the two to mate with one another can be quite a job, since there is no tolerance from this alignment.
The latter mentioned misalignment difficulty has been overcome according to U.S. Pat. No. 3,574,472 issued Apr. 13th, 1971 to Reliure Industrielle S.T.D. According to U.S. Pat. No. 3,574,472 the head of a post is elastically engaged in an open ended undercut recess. Since both the head of the post or stud and the recess walls are of an elastic nature, the securing action is not as positive as that of a stiffer material. Furthermore, the continuous nature of the recess substantially decreases from its strength and its locking action on the head of the post.
The present invention relates to a binding system comprising a post provided with a head projecting from one side of the system and an opening having a blind ended mouth surrounded by a mouth wall for releaseably securing the head of the post at the other side of the system. The mouth is narrower and at the same time longer than the head with the head being stiff for forceably opening the mouth during insertion therein and removal therefrom and having an undercut base for receiving the mouth wall when the head is locked in the opening. The arrangement is adapted to provide outward lateral flexing of the mouth wall as the head is forced therethrough and inward lateral rebounding of the mouth wall at the side undercut base of the head when the head is releaseably secured within the opening without having to provide resilient material at the mouth wall.
As a result of the nature of the binding system in which soft flexible materials are not required to operate the system, there is an extremely positive locking action on the head of the post. Furthermore, since the mouth is elongated relative to the head and due to the fact that the head will lock when received anywhere in the opening, there are very little alignment problems compared to the standard dome-type fastener. However, it is to be understood that the mouth is not continuous and is completely surrounded by the mouth wall which substantially adds to the locking action of the mouth wall on the post head.